The present invention relates to a ring-type piezoelectric ultrasonic motor which is different from the Electro-magnetically driven conventional motors and that has applications in robotics, precise controlling xy stage for semiconductor fabrication and optics, and automation equipment. More specifically, the present invention relates to a ring-type piezoelectric ultrasonic motor that is driven by a frictional force between rotor and stator, and said frictional force is produced by a piezoelectric ceramics that applies an alternate electric field with an ultrasonic frequency (above 16 kHz).
The driving methods generally known for piezoelectric ultrasonic motors are operating either through a half-wave batch converter or a quarter-wave batch or several quarter-wave batch converters for the operating shaft with a smaller cross section.
As an efficient movement of the driving shaft, the energy from the longitudinal oscillation of the half-wave batch converter is converted to a rotational motion of rotor under the condition of S1/S2xe2x89xa75 (S1: cross section of the converter, S2: total cross section of the shaft) condition (UK Patent GB2023965 B Ultrasonic Oscillating System 1978).
The basic principle of an ultrasonic drive is using a ring-type stator for bending vibration. On one face of the stator, piezoelectric ceramics that generate a mechanical vibration in order to allow their progression in the form of a wave, are attached and at the other face, protruding teeth that transmit an ellipsoidal phase change to the driving shaft on the pressure between the stator and the rotor are formed.
Due to an increase in the height of the protruding teeth for a ring-type resonator (stator), the magnitude of bending vibration is magnified and partially the rotational force of the rotor increases.
One object of the invention is to provide a ring-type piezoelectric ultrasonic motor which increases the rotational force by magnifying the magnitude of the vibration of concentrically protruding teeth attached to a ring type resonator.
Another object is to provide a ring-type piezoelectric ultrasonic motor which magnifies the magnitude of the vibration of concentrically protruding teeth and the vibration speed of a ring-type resonator (a stator) that is in contact with a rotor, and which can effectively apply a compressive force between a stator and a rotor.